We propose to field test and validate PALMS (Physical Activity Location Measurement System), a behavioral measurement tool that we have developed with support from the Gene-Environment Initiative (GEI). We will do this in an ongoing R01 study among church going Latinas in San Diego County. PALMS uses data from concurrently worn Global Positioning System (GPS) devices and accelerometers to ascertain location, time and type of physical activity (PA) on an essentially continuous basis. By the time this proposed project begins we will have validated the processing algorithms in PALMS in a highly controlled study supported by a GEI Opportunity Fund Grant. We have also processed 7-day GPS and accelerometer data from over 2000 participants (700 adults; 800 adolescents; and 500 children) enabling us to statistically demonstrate the value of collecting GPS data in addition to accelerometer data. However, we have not yet assessed PALMS in an ongoing cohort (or prospective) study and thus have no information on staff or participant burden in real world use. The field based validation study we propose herein will be the logical next step to ensure that PALMS is feasible to use-by both research staff and research participants-in typical research settings, and that it provides valid information about what it is intended to measure: the geospatial and temporal characteristics of physical activity. Importantly, we have selected to perform this research in collaboration with Dr. Elva Arredondo, PI of an R01 examining a place based physical activity intervention among Latinos in San Diego. Dr. Arredondo is a Co-investigator on a multi-site NHLBI-funded prospective cohort study, the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), a major national study with one of its four sites in San Diego (others are in Miami, New York and Chicago). The PI of the San Diego HCHS/SOL is Dr. Greg Talavera and he is a proposed co-investigator on the project we propose. Thus, this project will help set the stage for HCHS/SOL investigators to incorporate PALMS into the HCHS/SOL. In addition, place based interventions like Dr. Arredondo's R01, that are designed to improve PA environments and encourage PA in the most supportive environments, can greatly benefit from more precise measures of PA in time and space. In this study we will: a) Demonstrate the usability of PALMS in a community-based R01 trial through two rounds of assessment with participants and research staff; b) Demonstrate that PALMS can collect more precise and valid data on continuous combined measures of physical activity (via accelerometer) and location- x-time (via GPS) than current survey methods; and c) that these data provide added value to researchers as they have greater ability to predict location-x-PA relationships than current GIS or survey based methods.